Digital cameras typically include high speed, expensive working memory for processing image data, and non-volatile internal and/or removable storage for storing image files. Many digital cameras use removable flash memory cards for storing image files. The working memory is preferably provided on the same ASIC (application specific integrated circuit) as the image processing circuitry, and thus is very expensive. In order to accommodate large working memories, the working memory would have to be implemented on separate integrated circuits, which is highly undesirable because it substantially slows access to the memory, which would slow down the operation of the camera, would require the use of additional complex interface circuitry in both the working memory and the processor circuits, and would require more battery power.
To give a numeric example, for a digital camera that generates images of 1024.times.1024 pixels with 24 bits of color image data per pixel, the amount of working memory required to store the entire image would be 3 megabytes (MB). Additional working storage would be required for processing the image. Given the power consumption and cost limitations associated with consumer market digital cameras, 3 MB is simply not a feasible amount of working memory, at least as of 1999.
It is well known in the prior art that digital images can be processed a portion at a time, instead of all at once, thereby reducing memory requirements. For instance, the DCT transform used for JPEG compression and encoding of images is traditionally used on tiles of 8.times.8 pixels. However, a well known problem with tiling an image for processing is that the tiling produces undesirable tile border effects. The border effects of DCT tiling in JPEG images are considered to be acceptable because the very small size of the tiles makes the tiling effect relatively unnoticeable to the human eye.
However, using very small tiles such as 8.times.8 pixels is not practical when using wavelet or wavelet-like transforms in place of the DCT transform. Wavelet-like transforms have been shown to provide significantly better data compression than the DCT transform, and therefore using wavelet-like transforms in digital cameras would be desirable if the tiling effect can be avoided while using a moderate amount of working memory.
It is an object of the present invention to provide a digital camera that process images using a moderate amount of working memory, such as 5 or 6 KB, by transforming the image data using a wavelet-like transform with moderately sized tiles, such as tiles of 32.times.32 or 16.times.32 pixels, while at the same time avoiding the generation of undesirable tile border effects.